Edible things are starting to appear in our garden (through John's efforts alone these days) and it occurs to me there are some things Science could invent to help gardeners:
Leaf-penetrating radar: for finding all those cucumbers that hide until they're too fat to use
Underground MRI: to show which carrots, beets, potatoes, etc. are big enough to pull
Rodent-discouraging pods: Before we get to them, critters have chewed a hole and taken out all the peas.
Shaper for peppers: The ones from the store are perfectly formed. Ours taste better, but they look like some weird science experiment.
Shut-off valve for cherry tomatoes, green beans, and zucchini: We're so excited for the first ones, but by mid-August we're desperate to give them away. Don't stop to ask for directions--you'll leave with a car full of vegetables!
You probably have suggestions too if you're a gardener.